In July, everyday is full. But, if you arrive early, you will be able to go to the most wanted attractions with just a few minutes in line.
Program yourself: if Magic Kingdom will open at 9am, you have to arrive at the parking lot at 8:30am. It will take at least 30 minutes from the moment you park your car, get the tram, then the monorail or the boat, clear security and finally enter the park.
Once you enter the park, cross it and go as far away as possible from the entrace, people usually start their day at MK near Main Street. Go to Pirates of os the Caribean, Splash Mountain, Thunder Mountain, or even Space Mountain (oposite the others if you check the map).
Use FastPass, it helps a lot. But at 4 or 5pm, there will be no FastPasses left, keep this on your mind.
If you arrive early, you will have lunch at 12pm, wich means you will be able to grab a table at any restaurant. After 1pm, you will seat on the floor.
Don't forget to check with your kids where they want to go